1. Field of the Invention
The present invention relates to a laser diode driving device and an optical scanning device.
2. Description of the Related Art
There has been proposed a technique related to a laser diode driving device, in Japanese Patent Laid-Open Publication No. H11-245444, in which the value of a bias current to be applied to a laser diode is determined based on two amounts of laser emission and current values corresponding to the respective amounts of laser emission.
However, the conventional technique has a problem with a method of calculating the bias current to be applied to the laser diode.
A laser diode, particularly a VCSEL (semiconductor vertical-cavity surface-emitting laser) sometimes has a current-light amount characteristic which assumes an extreme value as shown in FIG. 6. In a case where the current-light amount characteristic assumes an extreme value, when a threshold current value Ithc of the laser diode is calculated based on the two amounts of laser emission and the current values corresponding thereto, the threshold current value Ithc deviates from an actual threshold current value Ith by ΔI as shown in FIGS. 7A and 7B.
A bias current value Ib is calculated based on the obtained threshold current value Ithc, and hence the value Ib to be set close to the target value Ith deviates therefrom. When the bias current value deviates from the target value, the light emitting characteristics of the laser become unstable. For example, when the laser is used in an optical communication apparatus, troubles occur in data transmission. Further, when the laser is used in an image forming apparatus, variation occurs in output of highlight-side density depending on the environment.